FIELD OF THE INVENTION
With contemporary smart cards, the semiconductor chip is fitted, by a carrier element usually formed with a non-conducting flexible substrate, into the smart card that is usually made of plastic. Not only the semiconductor chip, but also the contact faces, by which a reader can connect to the semiconductor chip, are disposed on the carrier element. To this, a surface-finished copper foil is usually laminated onto the non-conducting substrate and, for example, structured by etching. Before the lamination, holes are stamped into the non-conducting substrate, through which the chip can be electrically connected to the contact faces, for example using wires in the wire bond technique. The semiconductor chip and the wires are then covered by a protective encapsulation compound.
The smart cards need to be able to withstand particular bending loads, specified by the user. The bending forces which occur in this case must, however, be kept away from the chip since it is substantially more brittle than the material of the card. This is relevant, in particular, for chips that are larger than about 10 mm.sup.2. From European Patent EP 0 484 353 B1 it is known to provide a stiffening frame on the flexible substrate, which frame has a substantially greater bending stiffness than the flexible carrier substrate.
FIG. 4 shows an embodiment according to European Patent EP 0 484 353 B1. The non-conducting, flexible carrier substrate is provided with recesses. A foil is laminated onto the substrate by an adhesive. The foil is structured into contact faces, electrically insulated from one another by grooves. A semiconductor chip is adhesively bonded onto the substrate and is electrically connected to the contact faces by wires. In order to stiffen the flexible substrate, a stiffening ring is adhesively bonded onto the substrate. The interior of the stiffening ring is filled with an encapsulation compound, in order to protect the chip and the wires.
It is difficult to fit the stiffening ring, since there are relatively large positional tolerances and, in addition, the fitting operation requires special, elaborate tools. The overall result is very difficult and requires elaborate process control. Furthermore, the area needed for adhesively bonding the carrier element onto the card is restricted by the known stiffening ring.
U.S. Pat. No. 5,147,982 presents a carrier element in which a plastic sheet, which has an integrally formed strengthening and protective frame, is laminated onto a stamped metal grid that forms contact faces.